THREE DIMENSIONAL ANTENNA SYSTEM FOR MEASURING OSCILLATORY ELECTRIC FIELD STRENGTHS
A new three dimensional dipole based antenna system is described used to measure oscillatory electric field strengths. The antenna system is connected to an object (a survey platform) that is stationary or moving in an area of interest in air, over land, on water or under water. This invention aims to reduce the influence of noise sources on electric field strength measurements. Such measurements are generally collected as part of prospecting surveys for minerals or hydrocarbons.
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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT (IF APPLICABLE)Not Applicable
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BACKGROUND OF THE INVENTIONDiverse geophysical processes such as seismic and micro-seismic activity, volcanic activity, electric discharges from thunderstorms, vibrations introduced by human activities, and other phenomena cause propagating electromagnetic (EM) vibrations in the earth. The propagation and damping of these electric (E-type) and magnetic (B-type) emissions depends on the physical properties of the material in the earth. Differences in the local strength and phase characteristics of these electromagnetic vibrations can be used as indicators for the presence of hydrocarbons or minerals. These E-type and B-type oscillatory emissions always occur together. They can be measured separately by different sensing systems. My invention only concerns the antenna system used for E-type signals.
Moving survey platforms are used to collect such oscillatory electric signals using a three dimensional dipole antenna system. This antenna system is attached to a stinger or specially designed attachment. In what follows we have also used “stinger” for simplicity as a convenient reference for a specially designed attachment. The survey platforms may consist of manned or unmanned aircraft, drones towed behind aircraft, drones suspended under helicopters, drones towed behind ships, ships, cars, trucks or a stationary object. Suitable electronic equipment is used to digitize and store these signals. The frequency of the signals of interest is in the order of 0.01 Hz to approximately 300 Hz. This invention concerns the antenna sensor system used to collect the oscillatory electric field strengths. Although the description of this invention focuses on a moving survey platform, the same antenna system can be applied to a stationary survey platform.
A description of prior art on which the currently used technology is based can be found in representative patents and patent applications. Examples of patents describing such technology are for example: 1) U.S. Pat. No. 7,002,350, U.S. describes a three dimensional antenna system for a marine oil and gas exploration survey system, 2) U.S. Pat. No. 6,765,383 B1 describes a similar airborne system for drones, and 3) U.S. Pat. No. 4,945,310 describes a single dipole antenna system of a geophysical prospecting tool used to detect electromagnetic radiation. Such a system is not of concern for my invention.
Patent 1) and 2) rely on three curved dipole plate antennas for the measurement of E-type signals. Such antennas do not have uniform directional characteristics about their axis. Such a curved plate antenna system cannot measure the E-type field strength vector in three dimensions as easily and accurately as rod type antennas in a three dimensional dipole configuration. In addition, wires and other electronic equipment are usually located in the area of the antennas, such as inside a stinger. This produces noise on nearby (curved) plate antennas. To obtain a higher signal to noise ratio it is best to move such antennas away from these noise sources and use antennas that point away from the noise source. My invention is based on the need to improve the directional as well as the noise characteristics of the antenna system.
BRIEF SUMMARY OF THE INVENTIONThis invention describes a three dimensional antenna system used to measure oscillatory electric field strengths used in certain survey systems to explore for the presence of commercial quantities of hydrocarbons and minerals. The antenna system is located on a survey platform. My invention is a response to the need to improve the directional characteristics as well as the signal to noise ratio of such antenna system. This invention advances to the state of the art by introducing practical design improvements to a three dimensional set of dipole antennas that improve the signal to noise ratio of the measurements.
The first dipole antenna system consists of a rod antenna 14 and a specially designed half of a dipole antenna here simply depicted as a sleeve 15 shaped plate or foil antenna wrapped around an object depicted as a stinger 10 in
The antenna 15 may also be placed in close proximity of the inside wall of the stinger, its location in relation to antenna 14 is not critical and the axes of rod antenna 15 and sleeve 14 do not need to coincide or even be parallel. The antenna is made of a conducting material and in its cross section it loops around. Thus, for example if mounted on the outside of a circular stinger it would run around the stinger. Antenna 15 may be pierced by, but not limited to, other antennas fins or air foils as long as these do not electrically connect to antenna 15. If a circular electrical path around the stinger 10 is interrupted if such an item is large and it is impractical to maintain such a circular electrical path around the stinger then the different parts of antenna 15 would be electrically connected by wires.
In the general Y (12) direction, depicted in
In the general Z (13) direction, depicted in
The angular rod antenna offset 18 helps prevent or reduce antenna vibrations, which could cause erroneous measurements.
Rod antennas consist of a generic antenna with a length determined by what is practical for use on the survey platform. Generally the rod antenna length will be in the range of approximately ten centimeters to over two meters. Rod antennas may consist of a wire, a stiff rod, a telescoping rod or other designs. The surface of the rod antennas may have designs on them that have the purpose to reduce vibrations in an air flow. All rod antennas are made of a mechanically strong and conducting material similar to the way conventional car antennas are made (For a car the car antenna is one half of the dipole while the car usually forms the other half). The rod antennas and the plate or foil antenna may be electrically insulated by some coating to prevent direct contact with the air or water around them.
The purpose of electrical measurements collected from a stationary or moving survey platform is to obtain the strength of the local electric field strength vector. This requires a three dimensional antenna system. Only oscillatory data are of interest. Data usable to calculate corrections for noise to the strength of the local electric field strength vector measurements are not usually available. Examples of sources of noise to electric field strength measurements are electric discharges from the survey platform, motion of the antenna system in the earth magnetic field caused by irregular motion of the survey platform, antenna vibrations, other electric components placed in the stinger or near the antenna system, and other causes. This invention aims to reduce the influence of these noise sources to electric field strength measurements.
Electric discharges from the survey platform are already minimized by the designers of such craft by certain design features. However they cannot always be entirely prevented. In our invention their influence to electric field strength measurements is minimized by using the metallic part of the survey platform as ground to the electronic system and two separate additional antennas as a dipole antenna system.
Antenna vibrations can be caused by lateral air or water flow around an antenna. These vibrations in the earth magnetic field cause noise in the electric measurements by induction. These vibrations can be minimized by providing for antenna rod surfaces that are not smooth or/and by placing the antennas at a slight angle 18 such as depicted in
Electric components placed in the stinger or nearby the antenna system may emit electromagnetic radiation in the frequency range of interest to the electric measurements. Shielding of such components by metallic wraps or other methods may help reduce the noise from such systems to the electric field strength measurements. We found that the plate antenna 15 depicted in
This invention can also be applied to stationary survey platforms. The preferred direction of dipole antenna rod 14 of
It will be understood that the above-described embodiments of the invention are illustrative in nature, and that modifications thereof may occur and be made by those skilled in the art. Accordingly, this invention is not to be regarded as limited to the embodiments disclosed herein, but is to be limited only as defined in the appended claims.
Claims
1. A three dimensional antenna system for use on a survey platform was invented that is used to measure oscillatory electric field strengths in air or under water consisting of three independent dipole antennas referred to as antenna one, two and three with axes that are generally mutually perpendicular but not necessarily intersecting.
2. A dipole antenna as in claim 1 in which dipole antenna one consists of a rod antenna generally pointing in the direction of flow of the air or water past the rod antenna for moving systems and upwards for stationary systems and a sleeve shaped plate or foil antenna that is wrapped around an object such as, but not limited to a stinger, aircraft wing tank, a towed object or stationary object.
3. A sleeve shaped plate or foil antenna as in claim 2 in which the sleeve shaped plate or foil antenna may have an irregular shape and may have an axis that has no relation to the axis of the rod antenna of antenna one and is attached to material that qualifies as an electrical insulator.
4. Dipole antenna two and three as in claim 1 in which the dipole antenna two and three consist of two rod antennas each wherein the axes of the dipole antennas two and three are mutually perpendicular and the axis of dipole antenna two and three are approximately orthogonal to antenna one, while in moving systems the individual antenna rods are leaning by a small angle not exceeding thirty degrees in the air or water flow direction and in stationary systems the individual antenna rods would be sloped upwards by a small angle not exceeding thirty degrees.
5. The dipole antennas one, two and three as in claim 1 in which the distance between opposing antennas of the respective dipole antennas and the separation in perpendicular direction to the axes of the legs of a dipole antenna can be any practical distance with a maximum distance equal to the size of the survey platform.
6. The dipole antennas one, two and three as in claim 1 in which any rod antenna of the dipole antennas one, two or three may be placed where practical on, in or under the surface of the survey platform or inside any fin, wing or similarly shaped object of the survey platform if the survey platform has any.
7. The dipole antennas one, two and three as in claim 1 in which any rod antenna of the dipole antennas one, two or three may be replaced by a plate antenna where practical and may be placed on, inside or under the surface of any survey platform fin, wing or similarly shaped object of the survey platform if the survey platform has any.
8. The plate antennas as in claim 7 in which any plate antenna may have any practical shape and size that fits the shape of the fin or wing of the survey platform on which it is placed.
Type: Application
Filed: Jun 15, 2012
Publication Date: Dec 19, 2013
Inventor: Marius J. Mes (College Station, TX)
Application Number: 13/523,914
International Classification: G01V 3/12 (20060101);